1. Field of the Invention
The present invention relates to an ultrasound diagnostic apparatus, and more particularly to a technique for storing data in a memory section.
2. Description of Related Art
Most ultrasound (ultrasonic) diagnostic apparatuses used in the medical field include a cine-memory which is formed as a ring buffer or a temporary storage. A cine-memory stores data obtained through the transmission and reception of ultrasound. An ultrasound image is formed based on the data read from the cine-memory and the ultrasonic image is then displayed on a display device. Normally, the cine-memory stores data in units of one frame or one line. Here, one line corresponds to one ultrasound beam and one frame corresponds to one scan plane or one ultrasound image. A cine-memory generally has a storage capacity allowing storage of multiple numbers of frames obtained in time sequence. In a cine-memory, the newest input data overwrites the oldest data which is already stored in the memory, and this process is repeated.
When a freeze operation is performed by a user during real-time diagnosis, transmission and reception of ultrasound are stopped. In such a frozen state, it is possible to read data stored in the cine-memory and reproduce the data as a still image or a moving image. Because a cine-memory is generally stored on a volatile storage medium, the data content of the cine-memory is lost when the power of an ultrasound diagnosis apparatus is turned off. Further, due to the data overwriting as described above, data on the cine-memory is also lost sequentially. It is therefore necessary to save important data stored in the cine-memory. Accordingly, the data stored in a cine-memory is transferred to a non-volatile storage medium such as a hard disk or the like.
In a stress echo test, a patient is subjected to increasing stress in a series of steps by a physical or pharmaceutical method. Specifically, a test which is performed for one patient at one time includes a plurality of “stages”, and ultrasound diagnosis is performed from a plurality of “views” in each stage. More specifically, a “scene” is determined by a combination of a stage and a view, and a moving image obtained in ultrasound diagnosis (namely, in a capturing process) which is performed for each scene is stored. In this case, the image is stored in units of one heart beat, for example. After moving images for all the necessary scenes are captured and stored, the user selects a plurality of scenes for which images are to be reproduced. Then, a plurality of moving images corresponding to a plurality of scenes which are selected by the user are simultaneously reproduced in parallel to each other. The user can then compare and observe these moving images, whereby diagnosis of a disease concerning an organ such as the heart can be performed.
Japanese Patent Laid-Open Publication No. Hei 6-269455 describes an ultrasound diagnosis apparatus in which data obtained over a plurality of successive heart beats is transferred from a memory section to an external storage device. Japanese Patent Laid-Open Publication No. Hei 2-63447 describes an ultrasound diagnosis apparatus including a memory section which functions as a cine-memory. The storage region of the memory section is divided into two regions, each of which is used as a ring-buffer. Japanese Patent Laid-Open Publication No. Hei 2-63447, however, does not describe that the number into which the storage region is divided is variable in accordance with different ultrasound tests or a diagnostic states.
In each capturing process in a stress echo test, when a plurality of frames which are obtained are sequentially stored in a cine-memory, the stored data which was obtained in the past is to be erased by overwriting by new data, unless overwriting is prohibited with respect to the stored data. However, if prohibition of overwrite is set with regard to a great amount of data stored on the cine-memory in the preceding capturing processes, sufficient storage region cannot be secured in the subsequent capturing processes, thereby impairing completion of all processes of the stress echo test. Stated simply, the cine-memory runs out of a free space. On the other hand, when the amount of data stored in the preceding capturing process is reduced so as to secure a sufficient free space for the subsequent capturing processes, it is not possible to make effective use of the overall storage capacity over the entire stress echo test. In each capturing process, it is desirable to store, in addition to a moving image for a specific heart beat which is to be actually used for evaluation, a moving image for other heart beats as backup. However, conventionally, it is not possible for a user to appropriately determine the number of heart beats as the units of moving images to be stored in each capturing process. In a stress echo test, it is difficult to strictly predict the data amount to be obtained at the start of the test, because the heart rate changes with the change of stages.